Control system for starting an aircraft engine



Dec. 20, 1955 w. E. BRANDAU CONTROL SYSTEM FOR STARTING AN AIRCRAFTENGINE 3 Sheets-Sheet 1 Filed April 17, 1950 POWER SELECTOR LEVER I96REG. SPEED SELECTOR FUEL 27 REGULATOR rlli 6 FUEL i REGULATOR FIGJINVENTOR. W/LL/AM E. BRAND/4U Dec. 20, 1955 w E BRANDAU CONTROL SYSTEMFOR STARTING AN AIRCRAFT ENGINE Filed April 17, 1950 5 Sheets-Sheet 3FIG. 4

STARTER IGNITION g 309 L 306 303 N 32 l E E 3 IN VEN TOR. l V/L MM 5.BRAND/1 U W United States Patent Ofifice 2,727,356 Patented Dec. 20,1955 CONTROL SYSTEM or: STARTiNG Au AIRCRAFT ENGINE William E. Brandau,Westwood, N. J., assignor to Bendix Aviation Corporation, Teterboro, N.3., a corporation of Delaware Application April 17, 1350, Serial No.156,260

12 Claims. (Cl. 6039.14)

gas temperature and engine speed sensing regulator system. v

More particularly, the invention relates to improvements in and specificelectrical and mechanical means for control systems such as appear incopending application Serial No. 41,329, filed July 29, 1948, by WilliamE. Brandau, and application Serial N0. 90,453, filed April 29, 1949, byWilliam E. Brandau.

An object of the invention isto provide a novel starting'control systemincluding a plurality of speed actuated switches, one of the switchesbeing closed in starting to effect energization of the starter motor forrotating the compressor and energization of the ignition system for thecombustion chambers of the engine and the other switch being close d asthe. speed of the engine increases under power of the starter motor tocause the fuel cntrol valve to open to permit flow of fuel to thecombustion chamber and, the first mentioned being opened upon a furtherincrease in the turbine driven speed todeenergize the starter motor andignition circuit upon the fuel igniting. 1

The above and other objects and features of the invention will appearmore fully hereinafter from a consideration of the following descriptiontaken in connection with the accompanying drawings wherein oneembodiment of the invention is illustrated by way of example.

In the drawings: 7 v

Figure .l is a diagrammatic View of a typical turbine driven aircraftengine showing the take-off for the regulators of the respectiveturbines.

Figure 2 is aschematic diagram of the fuel regulator system for thecombustion chamber of one of the turbines.

Figure 3 is a fragmentary schematic drawingof a speed limitingmechanism.

Figure 4 is a fragmentary schematic view illustrating the rotarystarting switch in its initial position.

Figure 5 is a fragmentary schematic view fllustrating the rotarystarting switch in a second adjusted position.

Figure 6 is a fragmentary schematic view illustrating the rotarystarting switch in its final adjusted position after starting of theturbine engine has been elfected.

Turbo-jet engine Referring to Figure 1, there is mounted within the bodyof an aircraft a pair of exhaust gas driven turbines 3 for driving apropeller 5 of the aircraft as hereinafter explained.

The aircraft moves toward the left as viewed in Figure 1 so thatambientair is rammed into intakes 6. The air from the intake 6 is compressed bya blower or compressor 8 and flows through a conduit 10 into acombustion chamber 12. Fuel at a controlled rate is fed through a line16 into the combustion chamber 12.

The products of combustion flow out through a nozzle 18 to drive aturbine wheel 20 which drives the compressor a; through a shaft 22.Gearing 24 and a shaft25 connect the turbine shaft 22 with the speedgovernor of the fuel regulator indicated generally by the numeral 27.Also controlling the fuel regulator is a temperature sensitive element28 at the air inlet 6. As hereinafter explained, the element 28 may be abimetallic element connected through a suitable flexible drive shaft 29to the fuel regulater 27. Another temperature sensitive element 30.,issuitably positioned in the combustion chamber 12 to sense thetemperature of the combustion chamber gases. The element 39 may be asuitable'thermocouple electricallyconnected by leads 32 to the fuelregulator 27 as hereinafter explained. v

The drive shaft 22 is connected through a suitablesolenoid operatedclutch 35 and gearing 36 and 37 to a suitable drive shaft 38 for thepropeller S. The clutch 35 is controlled by a switch 39 controlling acircuit to energize the solenoid clutch 35 and effect a driving relationbetween the shaft 22 and the propeller shaft 38.

A propeller pitch governor 4%) of conventional type.

controls the pitch of the blades of the propeller 5 so as to regulatethe speed of the propeller to a predeterminedvalue which may be selectedby adjustment of a control lever 42 operably connected to the governor46 through rod 44 connected to a speed setting arm 46 of the propellerpitch governor 4 Selector lever 42 may be operated by the pilot inflight or by suitable automatic pilot control means.

The lever 42 is also operatively connected through linkage 48 to lever59 of the fuel regulator 27 for selecting the temperature setting of theregulator for each turbine engine in coordination with the selectedpropeller speed as hereinafter explained.

There is further provided a manually operable lever 51 connected throughsuitable linkage to lever 52 of the fuel regulator 27 for selecting thespeed setting of the regulator as hereinafter explained.

The turbo-prop fuel control system herein described serves to controlthe flow of fuel to the combustion chamw bers 12 of the two turbinesjointly geared to run at the same speed and to drive a propeller 5 of anaircraft. in which the speed of the propeller 5 is controlled by aseparate propeller pitch governor of conventional type. V

A separate fuel regulator 27 is provided to control the flow of fuel toeach combustion chamber in response to the combustion chambertemperature, turbine speed and other factors as hereinafter explained.

Fuel regulator bine to produce critical temperature damping and a speedlimiting signal which acts to maintain the turbine speed within apredetermined safe range.

For starting, ground idling operation and reverse propeller pitchoperation, the control may be changed by a manually operable bank ofswitches (as the speed lever 51 leaves its maximum position) to anentirely separate speed control system including a null-seeking loop ofselector voltage speed signal and valve follow-up voltage (without resetin this case in order to maintain a balance between the two powersections) which acts through a phase selector to saturate and overrideany existing temconnected through a shaft 53 to a rotor 55 of a variablecoupling transformer 57. The rotor 55 has a Winding 59 connected acrossa main source of alternating current having a constant frequency. Therotor winding 59 is inductively coupled to a stator winding 61. Thecoupling relation between the rotor and stator windings varies with theposition of the control lever 50.

The winding 61 is grounded at one end by a conductor 62 and a stallcomputer output winding 63 is connected at the other end by a conductor65 in series with the winding 61. The opposite end of the winding 63 isconnected by a conductor 67 in series with a secondary winding 69 of asaturable reactor 71 having a primary winding 73 and a control winding75. The primary winding 73 is connected by conductors '77 and 79 acrossthe main source of alternating current. Output conductor 32 leads fromthe temperature probe or thermocouple 30 to the control winding 75. Thetemperature probe 39 may be of a conventional type or of a type such asshown and described in the U. S. Patent No. 2,483,350, granted September27, 1949, to William R. Polye and William E. Brandau and assigned toBendix Aviation Corporation.

As shown in Figure l, the thermocouple 30 is positioned in thecombustion chamber 12 and the amplitude of the voltage induced insecondary winding 69 by winding 73 is a function inversely of the amountof D. C. current fed to the control winding 75 by the thermocouple 30 inresponse to the temperature of the combustion gases in the combustionchamber 12. Thus, upon an increase in the temperature of the combustiongases in the chamber 12, the D. C. voltage across the line 32 of thesaturating or control coil 75 increases causing in turn a decrease inthe voltage induced in the secondary winding 69 by the primary winding73, while a decrease in the temperature of the combustion gases in thecombustion chamber effects an increase in the induced voltage insecondary Winding 69.

The voltage induced in winding 69 is 180 degrees out of phase with thatinduced in the temperature selector winding 61 and that induced in thestall computer output winding 63 so that when out'of balance adifferential or signal voltage is applied to a control grid 85 of anelectronic mixing tube 87 through a conductor 89. The voltage induced inwinding 61 calls for a decrease in temperature and the voltage inducedin winding 69 calls for an increase in temperature.

The mixing tube 87 is of the type having rnulti-grids 85 and 91 and acommon anode and a battery or source of plate voltage 93 groundconnected at 94, all of which are well known in the art. The output ofthe mixing tube 87 is the resultant of the voltages applied to therespective grids 85 and 91 and the output of mixing tube 87 is appliedthrough input conductor 96, ground connection 94 and a grounded inputconductor 95 to an ampiifier 97. The amplifier 97 may be of aconventional type or may be of a type such as shown and described in U.S. Patent No. 2,493,605, granted January 3, 1950, to Adolph Warsher andassigned to Bendix Aviation Corporation.

. Output conductors 99 and 101 lead from the amplifier 97 to a magneticamplifier 103 of conventional type or of a type such as shown, forexample, in the U. S. Patent No. 2,432,036, granted December 2, 1947, toPaul A. Noxon and assigned to Bendix Aviation Corporation.

Output conductors 105 and 197 lead from the magnetic amplifier 103 tothe control winding of a two phase motor 109. The other winding of themotor 109 is connected 4 by conductors 111 and 113 across the mainsource of alternating current.

The motor 199 adjusts through a shaft 115 a fuel throttling valve 117 ina fuel conduit 16 to control the fuel supplied to the combustion chamber12. The fuel throttling valve 117 may be of a conventional type or maybe of a type such as disclosed and claimed inthe copending applicationSerial No. l58,l70, filed April 26, 1950, by Arnold H. Block andassigned to Bendix Aviation Corporation, now Patent No. 2,716,862.

Upon the temperature of the combustion chamber gases decreasing belowthat for which the temperature selector variable coupling transformer 57is set, a differential signal voltage will be applied by the winding 69to the grid of the mixing tube 87 and from the output of the mixing tube87 to the amplifier 97 and magnetic amplifier 103. The signal voltagewill be impressed across the motor control lines and 107 of such a phaseas to cause rotation of the shaft and adjustment of the fuel throttlingvalve 117 in a direction to increase the supply of fuel to thecombustion chamber 12 to in turn increase the temperature of thecombustion chamber gases to the selected value.

If the temperature of the combustion chamber gases increases above thatfor which the variable coupling transformer 57 is set, the signalvoltage across lines 105 and 107 originating from the dominatingdifferential signal voltage applied by winding 61 will have an oppositephase relation causing rotation of the motor 109 in an oppositedirection to decrease the fuel supplied to the combustion chamberthrough the throttling valve 117 and thereby decrease the temperature ofthe combustion chamber gases to the selected value. It will be seen,then, that the voltage of the temperature selector variable couplingtransformer 57 opposes that induced in the temperature responsivewinding 69 and the predominating signal voltage, of course, controls theaction of the motor 109 and tends to maintain the temperature selectedthrough the variable coupling transformer 57 by the position of thepilots control lever 42.

Stall computer The function of the stall computer and reset indicatedgenerally by the numeral is briefly to determine the maximum permissiblecombustion temperature which may be maintained without compressor surgeas a function of ram air temperature and turbine speed compared to theselected temperature and (:1) reduce the selected temperatureacccordingly if its too high or (b) make no change if the selectedtemperature is within a safe range.

Under the invention, in order to avoid the stall region of thecompressor which varies with inlet temperature and compressor speed,there has been devised an inlet temperature sensing device and acompressor speed sensing device which varies the maximum permissibletemperature so as to avoid stall conditions in accordance with apredetermined schedule. This schedule, of course, is dependent upon thecharacteristics of the particular engine to be controlled.

The schedules generally follow a given pattern so that as inlettemperature increases, the temperature sensing device tends to increasethe ceiling temperature or maximum permissible combustion chambertemperature. However, as the speed of the compressor increases fromidling to full throttle, the speed sensing device first tends todecrease the ceiling or maximum permissible temperature and then tendsto increase the ceiling or maximum permissible temperature as fullthrottle is approached in accordance with a predetermined schedule toavoid stall conditions of the engine.

Referring then to Figure 2, there is shown the stall computer circuit inwhich the stall computer output winding 63 is inductively coupled to arotor winding 127 connected across the main source of alternatingcurrent. The winding 12'! is rotatably positioned relative to the outputwinda ea-89B in 6? by ashaft .1 9 dr ve y c ven ona -phas zmpt 1 ha in a[fi s W n n c nn cte by o ductors 131 and 133 ,across the main source ofalternating rrent and a control winding connected through conuctors ;135and 137 to the output ofva computer amplifier 1319 which may be ofconventional type. V

The input to the computer amplifier includes grounded line 1451 and aconductor 143 seriallyzconnected through ,a ram air temperatureresponsive winding 145 and turvbinelspeed sensitive winding 147 andconductor 149 to conductor .67 leading serially to the temperatureselector winding-Q1 through the stall computer output winding 63.

The speed sensitive winding 147 is inductively coupled to arotorwinding151 connected across the main source of alternating current and.adjustably positioned relative Ito-the winding 147 and additionalstator windings 153 and 1-55 bya shaft 15? positioned byspeed responsiveiiyball governor 159. The governor 159 is in turn connected fluou h theShaft 25 to ,the turbine driven shaft 22 so .that the position of :therotorwinding 151 in relation to t he stator windings 14.7, 153 .and andthereby the voltage induced in such windings varies in relation .tothe.speedcfthe turbineizfl.

Inductively coupled with the ram air intake temperature sensitivewinding 145 is a rotor winding 161 having one end thereof grounded bythe conductor 163 while the opposite end is connected through aconductor 165 to the :stator winding 153. The opposite end of the statorwinding 153 is grounded vb-y a conductor -167 so that winding i153 and.16 1 .form a closed loop circuit. The speed responsive Winding 151 willinduce into the winding 153 a signal voltage depending upon the speed ofthe turbine 20 which signal voltage will be in turn induced by thewinding 161 into the .winding 145 in a value depending upon ithe:adjusted position of the rotor winding-161 which is controlled througha flexible shaft 29 by the bimetallic ram air inlet temperaturesensitive device 28. The voltage inducedin .the speed sensitive winding147 will act in opposition to the voltage induced in the temperatureselector winding 61 while that induced in the compressor air inlettemperature sensitive winding 145 will be a function of speed and ramair inlet temperature andhaving a phase relationship acting in additiverelation with the signal voltage induced in the turbine speed responsivewinding 147.

In the event the additive voltage induced in the wind- ;ings 147 and 145exceeds the voltage induced in the temperature selector winding 61indicating selection of a temperature within the stall range, thedifferential signal voltage applied to the stall computer amplifier 139will then cause the actuator motor 130 tocrank the rotor 127 as requiredto maintain a Zero voltage around the reset loop, and thus reduce theselected temperature to the level dictated by the stall computer. Thereverse action of increasing the selected temperature to the stall levelis prevented by incorporating a zero stop .on the rotor 127 preventingrotation .of the rotor 127 ina direction such iasto increasethe selectedtemperature.

7 The stator windings 147 and 153 are so arranged in relation to therotor winding 151 that as thecompressor increases from idling to fullthrottle, the speed sensing device :159 :fiISt adjusts the rotor winding151 so as to first-tend to decrease the ceiling or maximum permissibletemperature with increase in speed and then tends to increase theceiling temperature with further increase in speed so as-to match apredetermined ceiling schedule to avoid stall conditions dependent uponthe characteristics of the particular engine controlled while thetemperature sensing device 28 tends to increase the ceiling temperatureas inlet temperature increases to match the ceiling schedule.

Selective auxiliary control circuits ,Asshown in Figure 2, the output ofthemixing tube 87 6 is contr l d ibvs d b a ed by t e pera u e r sp sivecontrol circuit described and by the grid 591.

In order to control the signal voltage applied to the grid 91 there areprovided two auxiliary loop circuits which may alternately beselectively connected to the control grid 91 through operation of a gangswitch 174 (Figure 1), including switch element 175 controllingcontrolling contacts 176, and 177, switch element 179 controllingcontacts 180 and 181, switch element 183 controlling contacts 184 and185, and switch element '18? controlling contacts 188 and 18 9.

As shown in Figure 1, when the speed selector lever 51 is moved to itsmaximum speed selecting position, a projection 190 thereon is arrangedto contact an arm 192 mounted on .a shaft 194 for actuating in unisonagainst the biasing force of a spring 196 the several switch elements175, 179, 183 and 187 so as to close contacts 176, 180, 184 and 188 andopen contacts -177, 181, and 189 controlling the fuel regulators 27 andtransfer the control of the respective fuel regulating valve 117 from abasic speed control to a separate temperature control as will beexplained hereinafter. Within a lower speed rangeadjustment of the speedselector lever 51, the switch elements 175, 179, 1.83 and 187 are heldby spring 196 in the position shown in Figure 1 closing contacts 177,181, 185 and 189.

In normal operation, the speed selector lever 51 is adjusted to themaximum speed selection position and the switch elements 175, 179, 183and 187, as shown ,in Figure 2, close the respective contacts '176, 180,184 and 188, whereupon the control of the .fuel regulating valve 117 isunder basic temperaturecontrol in which th conrol grid 91 is biased by asignal voltage resultingfrom an off-speed coupling to givespeed-temperature interaction stability, ,fuel valve position follow-upand reset signals to produce critical temperature damping and anover-and-under speed signal.

The auxiliary circuit affecting such signal voltage includes in serialrelation the switch 175 closing contact 176, speed selector windingl98,speed stabilizing winding 155, switch 179 closing contact 180, speedlimit control winding 200, switch 183 closing contact 184, temperaturereset winding 202, and temperature follow-up winding 204 groundconnected at 206 to the input ofthe mixing tube 87 through the groundconnection 94 of the battcry;9.3l.

inductively coupled to the speed selector winding198 is a rotary winding210 connected across the source of alternating current and operativelypositioned relative to the winding 198 through a shaft 212 positioned bythe speed selector lever 52 which, as shown in Figure 2, is in themaximum speedselecting position. The winding 210 is arranged to induceinto the winding 198 a voltagelSO degrees out of phase with the voltageinduced in the winding 155 by the turbine speed responsive rotarywinding 151. The voltage induced in winding 198 calls ,forvthe fuelvalve 117 to close to eflfect a decrease in speed while the voltageinduced in winding155 calls for -the fuel :valve 117, to opento effectan increase in speed. As the winding 210 is adjusted to select maximumspeed, :the differential voltage induced in winding 155 normally callsfor fuel valve117 to open to effect an increase in speed and temperatureuntil the maximum selected speed isatrained when the voltage induced inwinding 198 ,tends to hold the speed to the maximum selectedspeedsubject, however, at all timesto the action of the maintemperaturecontrol circuit which applies ,a signal voltage, tozthe grid85 tending to hold the temperature within the selected temperature valuesubject to the monitoring effectof the stall computer.

The basic temperature control circuit is an off-speed signal tostability.

thus biasedby give speed-temperature interaction 1" emperazu rrevfollowup ,As shown in Figure 2, themotor-109, in addition .topositioning the throttle valve 117 through shaft11.5,.also

7 positioned through a shaft 215 a rotor winding 217. The rotor Winding217 is connected through suitable conductors to the main source ofalternating current. The

winding 217 is further inductively coupled to the temperature follow-upstator winding 204 and a second stator winding 219. The winding 217 isarranged to induce in the Winding 204 a voltage which is in phase withthe voltage induced in the winding 198 and 180 degrees out of phase withthe voltage induced in the winding 155 so as to tend to add to thevoltage induced in the winding 198 a follow-up voltage which increasesupon adjustment of the rotor winding 217 by the motor 109 in a valve 117opening direction to increase fuel engine speed or temperature andtending to re-balance the difierential or signal voltage across thelines 105 and 107 occurring upon unbalanced relation between the voltageinduced in the windings 61 and 69 and windings 198 and 155. Upon a callfor decrease in fuel engine speed and temperature the motor 217 isadjusted in an opposite valve closing direction and tending to decreasethe additive effect of the voltage induced in the follow-up winding 204and efiecting a reverse follow-up action. The follow-up actionaforenoted occurs relatively rapidly upon adjustment of the throttlingvalve 117 by the motor 109 to give a well damped control to thethrottling valve 117.

Temperature reset action A further temperature reset action is efiectedthrough operation of a temperature reset rotary winding 222 connectedthrough suitable conductors across the main source of alternatingcurrent and inductively coupled to temperature reset winding 202 so asto induce a voltage therein which opposes the voltage in the temperaturefollow-up winding 204. The follow-up droop is removed by a slow speedreversible electrical reset motor 224 which drives the rotor winding 222through a shaft 226 and in a direction to slowly remove the errorbetween the selected temperature and the actual temperature introducd bythe follow-up winding 204. Th rotor winding 222 is relatively slowlyadjusted by the motor 224 which may be of the conventional two-phasetype having a winding connected through conductors 228 and 230 acrossthe main source of alternating current and a control winding connectedby conductors 232 and 234 to the output of an amplifier 236. The resetamplifier 236 may be of conventional type or may be of a type such asshown and described in the aforesaid U. S. Patent No. 2,493,605.

The input to the amplifier 236 includes a grounded connection 238 and aconductor 240 connecting the input of the reset amplifier 236 in a loopcircuit including tem- I perature reset winding 202 and a temperaturefollow-up winding 204 so that a differential or reset signal voltage isinduced across input lines 238 and 240 having a phase relationshipdependent upon whether the fuel valve 117 has been adjusted in a fuelopening or fuel closing direction.

Thus the signal voltage applied by the amplifier 236 to the controlwinding of the motor 224 will cause rotation slowly of the rotor winding222 in a direction to cause the induction in the temperature resetwinding 202 of a reset voltage tending to oppose and wipe out thefollow-up voltage induced in the winding 204. The voltage induced by thewinding 217 in the winding 204 is opposite in phase to that induced inthe winding 202 by the winding 222 so that the follow-up movement of thewinding 217 to increase the voltage induced in the motor 224 will befollowed up by a slow rotation of the rotor winding 222 in a directionto induce in the winding 202 an increase in voltage of opposite phase totend to wipe out the follow-up voltage induced in the winding 204.

Speed limit control Inductively coupled to the speed limit controlwinding 200 is a rotary winding 250 connected by suitable conductorsacross the main source of alternating current. The

rotary winding 250 is operatively positioned relative to the winding 200by a rotatable shaft 252 to which there is secured at one end an arm 253normally held by springs 254, as shown in Figure 3, in a neutralposition at which the rotor winding 250 will induce zero voltage in thewinding 200. A pin 255 carried by arm 256 of shaft 157 is arranged sothat at the extreme of counterclockwise rotary movement of the arm 256the pin 255 will strike the arm 253 at one side so as to actuate arm 253against the force of springs 254 in a counterclockwise direction uponthe shaft 157 being rotated by the fiyball governor 159 in response tothe speed of the turbine exceeding a predetermined maximum speed andthereupon the winding 250 is adjusted by the mechanism 252, 253, 255 and256 into inductive relation with the winding 200 so as to induce thereina signal voltage affecting the control grid 91 in such a sense as tocall for the motor 109 to actuate the fuel throttling valve 117 in aclosing direction to decrease the speed of the turbine to withinthepredetermined safe value. Features of the speed limit control arefurther described and claimed in a copending United States applicationfor Patent Serial No. 248,672, filed September 28, 1951, by William E.Brandau and assigned to Bendix Aviation Corporation.

Operation of auxiliary circuit the speed and temperature setting of theregulator upon the speed of the turbine 20 exceeding a predeterminedmaximum value as during maneuvers of the plane, as ex- 1 plained in thecopending application Serial No. 248,672.

Regulator speed selection operation For starting ground idle and reversepitch operation, the control is changed by manual switching (as theregulator speed selector lever 51 leaves its maximum position) toan'entirely separate speed control system. 7

In the latter adjusted position of the lever 51,'the gang switch 174, asshown by dotted lines in Figure 2, causes the switch to close thecontact 177 the switch 179 to close contact 181; the switch 183 to closecontact 185 and the switch 187 to close contact 189. In the latteradjusted arrangement of the several switch elements the cont act 177 isgrounded through a conductor 260 to connect one end of a speed controlcircuit to the input of an amplifier 262 through grounded connection263. The opposite end of the speed control circuit loop is connectedthrough switch 187 which now closes contact 189 to'input conductor 265of the speed amplifier 262. The speed control circuit includes the speedselector winding 198,-the speed responsive winding 155, and the speedfollow-up winding 219. As shown by dotted lines in Figure 2, in thelatter circuit the switch 179 closes contact 181 and switch 187 closescontact 189.

It will be seen from the foregoing that the speed control circuit nowacts through the speed amplifier 262 instead of controlling the bias onthe control grid 91 of the mixing tube 87. In this circuit the selectorwinding 198, and speed responsive winding 155 act in the mannerheretofore described and furthermore, there is induced in the speedfollow-up winding 219 by the rotary winding 217 a follow-up voltageacting in opposition to the voltage induced in the speed responsivewinding 155 in a manner similar to that of the winding 204 previouslydescribed which is now disconnected from the speed'com.

9 case in order main ain a balan e we n h tw p wer sec ion which act thrugh th sp d p fi 262. The amplifier 262 may be of the conventional typeor may be of a type such as shown and described in the aforesaid U. S.Pat. No. 2,493,605.

Output conductors 265 lead from the speed amplifier 262 to a phaseselector indicated generally by the numeral 267 and which may be of atype such as disclosed in the said copending application Serial No.41,329.

The phase selector 267 is so designed as to permit the passage of asignal voltage to output lines 269 and 270 of a phase corresponding tothat induced in the winding 19.8 and indicative of an overspeedcondition of the turbine 20, while preventing the passage of a signalvoltage of an opposite phase or a phase corresponding to that induced inthe winding 155 and indicative of an underspeed condition.

Thus a Signal voltage calling for more fuel or temperature maybe blockedout through action of the phase selector 267 while a signal voltagecalling for a decrease in fuel or temperature upon the turbine speedbeing in excess of that selected through adjustment of the winding 210may be passed through the phase selector 267 to output lines 269 and 270to input lines 99 and 101 of the magnetic amplifier 103. The lattersignal voltage serving :to decrease the fuel and temperature of theengine is of sufiicient amplitude as to override any signal voltage fromthe temperature responsive amplifier 97 tending to call for opening ofthe valve 117 to supply more fuel or increase-the speed of the engine.

It will be seen then that the action of the phase selector 267 is suchthat underspeed signals are blocked and increased fuel voltage signalsreach the servomotor 109 only in the form of an under-temperature signalthrough :the temperature amplifier 197. Thus all operation on the speedcircuit will be monitored during accelerations by the temperaturesetting on thestall computer.

It will be further seen that through adjustment of the switch 183 toclose contact 185, as indicated by dotted lines in Figure 2, thetemperature follow-up winding 204 and the temperature reset winding 202will effect a followup and reset signal voltage bias on the control grid91 of the mixing tube 87 as the fuel valve 117 is adjustably positionedthrough operation of the motor 109 by the temperature responsive systemwhen the speed of the turbine 20 does'not exceed the selected value.

The aforedescribed features are further described and claimed in thecopending United States application for patent, Serial No. 248,672.

Starting operation In starting, the regulator speed selector lever 51 isfirst adjusted to within a minimum speed selecting range, a furtheradjustment of the lever 42 to a minimum propeller speed and temperatureselecting position will cause a starter switch 300 to be closed as shownin Figure 1. The present application is directed to features ofapplicants novel control system for starting an aircraft engine.

The closing of switch 300 then completes a circuit as shown in Figure 4from a battery or source of electrical energy 302 through brushes 303and 304 of a rotatable electrical conductive member 305, and a manuallyoperated switch 306 to energize a starter indicated by the numeral 307and through a manually operable switch 308 to energize an ignitiondevice 309. The starter and ignition device are shown schematically andmay be of conventional type. Energization of the starter imparts rotarymovement to the turbine 20 of the engine in a conventional manner. Uponrotation of the turbine 20 reaching a predetermined minimum speed, theshaft 157 and thereby the rotary switch 305 is adjusted by the flyballgovernor 159 to the position shown in Figure 5 at which the brush 311moves off an insulation strip 313 carried by the conductive member 305of Figure 4 and closes through the conductive member 305 an additionalcircuit for energiz- 10 iugznn electromagnet 315 to actuate switch 317from the position shownin Figure 4 to the position shown in Figure 2against thebiasing force of a spring 318.

In the position shown in Figure 4, the switch 317 con- ;nects the inputof the amplifier 262 through a transformer 319 to the main source ofalternating current and providing a voltage phase causing motor 109 torotate the fuel valve 117 to a closed position. The actuation .of theswitch 317 to the position shown in Figure 2 connects the line 265through conductor 325 to the input of the amplifier 262 and permitsrotation of the motor 109 in an opposite direction opening the fuelthrottling valve 117 to the position called for by the regulating systemin nor mal operation and permits ignition by the ignition device 309 ofthe .fuel gases supplied the combustion chamber 12 through thethrottling valve 117, whereupon the starting operation of the turbine iseffected.

After the turbine has been brought to starting speed, further adjustmentof the rotary switch 305 by the fiyball governor 159 will cause therotary switch 305 to break the circuit at brush 304 through aninsulation strip 321 carried by the rotatable member 305, as shown inFigure 6. Upon the speed of the turbine reaching a desired speed, thesame may be drivingly connected to the propeller shaft 38 by closingswitch 39 to effect operation of associated clutch 35 so as to drivinglyconnect shaft 22 and the propeller shaft 38.

After one turbine 20 has been started and drivingly connected to thepropeller shaft 38, the other turbine 20 may in turn be similarlystarted or in the alternative may be started by manually opening switch306 and closing switch 308 of the ignition circuit for the othercombustionchamber 12 and drivingly connecting the other turbine to thepropeller shaft 33 through operation of the associated clutch 35 of theother turbine 20 by closing its control switch 39.

After the turbine engines have been started, the manual control 42 maybe adjusted to open switch 300 and set the combustion chambertemperature and propeller speed to the desired values while theregulator speed control 51 may be shifted to the maximum settingthereupon actuating the gang switch 174 and shifting the basic .controlof the fuel valve 117 for both regulators from speed control to thenormal basic temperature control.

Although only one embodiment of the invention has been illustrated anddescribed, various changes in the form and relative arrangements of theparts may be made to suit requirements.

What is claimed is:

1. For use in starting an aircraft engine having a fuel intake conduitfor said engine and a fuel control valve; the combination comprising anengine speed responsive mechanism, a switch means operated by saidmechanism for initially closing electrical circuits to a starting andignition device for said engine, means operable by said mechanism uponthe driven speed of the engine exceeding a predetermined value forclosing an electrical circuit for effecting opening of the fuel controlvalve to permit the fiow of fuel to said engine for starting, andadditional means operable by said mechanism upon the driven speed of theengine exceeding a greater predetermined value for opening the firstmentioned circuits for said starting and ignition devices.

2. The combination defined by claim 1 in which the switch meanscomprises a rotatable conductive member, switch brushes bearing on saidmember, and insulation elements carried by said member for selectivelyopening and closing said circuits.

3. For use in starting an aircraft engine having a fuel intake conduitfor said engine and means for controlling the supply of fuel throughsaid conduit; the combination comprising an engine speed responsivemechanism, switching means operated by said mechanism for affectingelectrical circuits to initiate operation of a starting and ignitiondevice for said engine, switching means operable by said mechansm uponthe driven speed of the engine exceeding a predetermined value foraffecting electrical circuits to initiate flow of fuel to said enginefor starting, and switching means operable by said mechanism upon thedriven speed of the engine exceeding a predetermined value fordiscontinuing the operation of said starting and ignition device.

4. For use in starting an aircraft engine having a fuel intake conduitfor said engine and a fuel control valve; the combination comprisingdriving means for imparting movement to the engine, ignition means forigniting the engine fuel, reversible motor means for opening and closingthe fuel control valve, relay means for controlling said motor means soas to normally maintain the fuel control valve in a closed position, anengine speed responsive means, a rotary switch driven by said speedresponsive means and controlling said relay means so as to cause themotor means to effect the opening of the fuel control valve upon thespeed of said engine exceeding a predetermined minimum value.

5. For use in' starting an aircraft engine having a-fnel intake conduitfor saidengine and a fuel control device; the combination comprisingengine temperature respon sive means, first means operatively connectingsaid temperature responsive means to the fuel control device so as tomaintain a selected engine temperature, a first adjustable controlmember for selecting the engine ternperature, engine speed responsivemeans, second means operatively connecting said speed responsive meansto said fuel control device so as to prevent the engine speed fromexceeding a selected maximum value at the selected engine temperature, asecond adjustable control iember for selecting the engine speed, meansfor imparting movement to start the engine, and control means forinitiating operation of said starting means and efiectire uponadjustment of said first control member to a minimum temperatureselecting position.

6. The combination defined by claim 5 in which the control meansincludes means effective to energize the starting means upon adjustmentof the first control member within a predetermined maximum temperatureselecting range.

7. The combination. defined by claim 5 including means for deenergizingsaid starting means, and means operatively connecting the deenergizingmeans to the speed responsive means for efiecting deenergization of thestarting means upon the engine speed exceeding a predetermined value.

8. The combination defined by claim 5 including means for igniting theengine fuel, means for deener- 12 gizing said igniting means, and meansoperatively connecting the deenergizing means to the speed responsivemeans for effecting deenergization of the igniting means upon the enginespeed exceeding a predetermined value.

9. The combination defined in claim 5 including means for igniting theengine fuel, means for deenergizing said igniting means and the startingmeans, and means operatively connecting the deenergizing means to thespeed responsive means for effecting deenergization of the'ignitingmeans and the starting means upon the engine speed exceeding apredetermined value.

'10. The combination defined by claim 5 including means for initiatingoperation of the fuel control device, means operatively connecting theinitiating means to the speed responsive means for effecting theoperation of said fuel control device upon the engine speed exceeding afirst predetermined value, means for igniting the engine fuel, means fordeenergizing said ignitingmeans and the starting means, and meansoperatively connecting the deenergizing means to the speed responsivemeans for effecting deenergization of the igniting means and thestarting means upon the engine speed exceeding a second higherpredetermined value.

11. The combination defined by claim 5 including other control means foralternately connecting said speed responsive means to said fuel controldevice through said first and second connecting means.

12. The combination defined by claim 5 including other control means foralternately connecting said speed fuel control device.

References Cited in the-file of this patent UNITED STATES PATENTS2,091,998 Lysholm Sept. 7, 1937 2,432,177 Sdille Dec. 9, 1947 2,452,298Oct. 26, 1948 2,476,213 Prime et al. July 12, 1949 2,479,813 Chamberlinet al Aug. 23, 1949 2,545,856 Orr Mar. 20, 1951 2,608,054 Price Aug. 26,1952 2,643,511 Briggs June 30, 1953

